Every day in Madison, about 300 trucks and cars drop off a thousand tons of trash at the Dane County landfill, on Route 12 just on the other side of the interstate from Madison. They come from towns and cities in the county, from local businesses and private individuals, and they drop off their waste here, at the 120 acre landfill for waste disposal.
Landfill director John Welch describes the site. “You can see here its a very busy place, we get anywhere from three hundred to four hundred customers in a day, so its very very busy. We are a government agency, but we are what’s called an enterprise fund, which means we run a lot like a small business. We do not use any taxpayer dollars and we never have in our 30 plus years of existence. All of these customers coming across the scale pay us to take their waste or their materials.”
Dane County’s landfill is owned by the county, and anyone can come and drop off their waste here. Trucks are weighed entering the facility, then weighed leaving, and are charged by the difference in weight. Some are huge semis packed to the gills with municipal waste. Others are small vans dropping off trash from small businesses, but the process is the same.
First there are a few things that can’t be landfilled that need to be sorted out. Tires and shingles are gathered in huge piles near the entrance. Welch explains that they can jeopardize a landfills health.
“In the event of hailstorm, for three months we get shingles shingles shingles, and it can cause problems in landfills, where it can almost create a roof inside the waste, and then liquid will travel out to the side slopes and lead to leaks or difficulty managing that,” said Director Welch. “Tires are very difficult to work with in a landfill. Anything made out of rubber works its way to the top of the waste. We have large equipment that is compacting and also vibrating, and as it vibrates, rubber keeps moving back to the top.”
As an added bonus, both shingles and tires can be recycled and reused.
Next comes what the landfill calls the Clean Sweep. This includes chemicals, electronics, paints and solvents, which are handled in a separate building. Kevin Belida, a hazardous waste coordinator for the landfill, explains how they handle acids and other dangerous materials: “So we get a lot of flammable liquids, bad gas, oil-based paint, that ultimately gets poured into a drum or sent off in a box to Violia’s our hazardous waste disposal contractor bulks it all into a larger tank, and it gets burned as an alternative fuel. So the flammable liquids get reused and recycled, same with the used oil and anti-freeze. Aerosol cans get crushed and punctured and same thing they get used as a fuel. Poison liquids and poison solids ultimately go for incineration. Acids and bases, they get neutralized. And stuff like the oxidizers and the more interesting lab-grade type chemicals, they go for incineration.”
The facility is designed to be safe even though lots of dangerous materials are present. The light fixtures are special no-spark lights. There are multiple fume hoods and ventilation fans. In case of explosion, an entire portion of the wall is thin metal, designed to blow out and relieve the force of explosive air to minimize damage. Electronics are bundled together and sent to an e-recycling facility. As part of the clean sweep, any container that is more than half-full is offered free of charge to anyone who wants to come pick it up — the large room held a number of household cleaners, as well as large amounts of paint for anyone who needs it.
Next to the clean sweep building is a building for Construction and Demolition Waste, which is quite different than municipal waste: typically concrete, wood, metal, drywall, and brick. According to estimates from the EPA, there’s nearly twice as much construction and demolition waste by weight than municipal waste. And almost all of that material can be recycled. The EPA estimates nearly 75% of all Demolition waste is recycled, as opposed to only 20% of municipal waste.
Part of that recycling happens at the Dane County Landfill. Large bulldozers push trash onto a conveyor belt on the second floor. Workers push the waste into dedicated holes next to the belt, dropping the waste down into large piles on the ground floor where they are picked up and taken to dedicated recycling facilities.
Director Welch explains: “So all those dumpsters of C and D material from job sites and construction sites they come in here totally commingled. There is a bunch of equipment and mechanical separation of that material, basically breaking it down by size. Next, there is a couple of conveyor belts, pick lines, where workers are grabbing materials. So as a material is going by on a conveyor belt, you might be grabbing one grade of wood, I might be grabbing metal, and we’re a dropping it through a hole in the ground into a bunker, and underneath is a small garage. You end up with clean wood in one garage, clean metal in one garage, rocks, bricks and aggregate in another.”
The building is a collaborative project between the landfill and Lakeshore Recycling, a private recycling company. The company finds buyers for the materials, while the landfill provides a useful dropping-off site.
“Its a great public-private partnership, we’re trying to capitalize on each other’s strengths. Dane County, we have this existing facility and infrastructure. We have a customer base that’s used to coming in to us and across our scales. We have relatively low financing with bonding on this facility,” said Welch. “Lakeshore Recycling, they’re really able to manage staff, and manage the materials on the back end. Markets shift a lot. If the price of wood drops in half next month, they can much quickly adjust and adapt to that. Put more R&D into what other products can we develop with this wood now? Can we build a new customer base with farmers for animal bedding rather than using it all for landscape mulch? And that’s a true example that happened five, six years ago.”
But the largest part of the landfill site is, of course, the landfill itself. The hill of trash rises 110 feet high, about ten stories, and is capped with a mixture of grasses designed to simulate local prairie. Near the facility, the hill looks like almost any other hill in Southern Wisconsin, except it rises steadily and unnaturally high.
About a five minute drive around the facility, though, and you are at the part of the landfill in use. The landfill is utilized in 12-acre increments called cells. Preparing a cell is an arduous process.
“There are a lot of layers that go into building this liner to make sure we’re protecting the environment, protecting the groundwater underneath the landfill. There is an underdrain system to make sure ground water doesn’t get up and erode the liner from the bottom. Then there is four feet of compacted clay that goes in in eight different lifts, and with each lift, the compactor spikes have to be longer than the lift, so it kneads that lift into the lift below it. And then the one above it gets kneaded into that. So you end up with 12 acres wide, four foot thick compacted clay. Once that’s all done. Then we put on the geo-membrane, which is a really really thick plastic, its a 60 mil. HDPE , high density poly-ethylene. Its about an eighth of an inch thick plastic roll. Its rolled out, and then there is a really thin fabric sheet to protect that liner. And you see here its all stone, so the final layer is this one foot thick layer of drainage stone.”
Once a cell is ready, trash is distributed evenly across the whole thing, at around two feet of height. This is the last opportunity to find things that shouldn’t belong in the landfill, mostly tires and shingles at this point. Large semis drive the trash from the drop-off stations out to the field, were they dump their load and bulldozers distribute it. After the layering is finished for the day, the trash is covered with a layer of dirt, to help with odors and keep out pests.
After two feet of trash is distributed across the whole thing, the process begins again, slowly building up a hill that will tower over the landscape. A new cell was just opened at the Dane County landfill, and it should take about six years to fill up. On the ground layer, the trash is not compacted; There is a danger that the process could damage the liner. But later layers will be compressed. A huge truck designed for this task will drive over the whole layer, crushing everything under its weight, and vibrating the whole thing with large spikes to help the trash settle.
This is the last cell available to the Dane County landfill. It is the farthest corner of the facility, and there is no more room to grow. The landfill is hoping for a height extension, that could add another three years of use, but nine years from now, the landfill will be full, and Dane County will have to open up a new site.
“Without that vertical expansion, we have about six years of site life left in this site, with that expansion we have about nine years. After that we see no ability to expand further at this site. We’re landlocked by roads and wetlands and other things. The rule of thumb in Wisconsin is that it takes about 10 years to site a new landfill site, so we need to be working on that very quickly,” said Welch.
If you look closely at the Dane County landfill you can see small clusters of pipes that emerge from the hill at regular intervals. At this landfill, they mine the methane that the organic waste produces. The entire landfill is kept slightly pressure-negative, and the pipes suck up the produced gases like a network of carefully calibrated straws.
Organic waste is the largest share of waste at the landfill by weight, making up nearly a third of all the waste landfilled there. And as that waste decomposes, it releases greenhouse gases, a mixture of Carbon dioxide and methane, with some other trace gases. Methane is an even more potent greenhouse gas, but unlike carbon dioxide, it’s also valuable. Methane is the main component of natural gas, and can be used as a biofuel. For a while, the Dane County landfill burned its methane to generate electricity, but now it refines it into a liquid fuel that can be used as vehicle fuel
“So what we’re doing now, is collecting all that gas, about 1800 standard cubic feet of gas every single minute. Its about 55 percent methane, so we need to pull out all the other things and get it up to 97 percent methane,” said Welch. “We can then inject it into the pipeline, we can use that pipeline to transport it to CNG fueling stations. Now we’ve shown that our gas is going to vehicle fuel, and can get credits through the EPA program. We’re producing a little over three million gallons of vehicle fuel every single year off of garbage gas.”
For the landfill, the sale of its methane is a large source of its revenue. The landfill is profitable and makes money for the county. The sale of biogas accounts for about 12 million dollars of revenue per year, and the landfill makes money two ways from its sale; first from the sale of the gas itself, and then again by selling the green energy credits to heavier polluters to offset their pollution.
The whole project required installing a natural gas injector at the landfill which hooks the site up with the national pipeline network. This allows the landfill to offer a unique service — agricultural digestors that process cow manure can drop off their own biogas, and the landfill processes their biogas for a share of the sale. This has led to a proliferation of agricultural manure digestors in southern Wisconsin, and now the methane from cow manure is captured instead of being pumped into the atmosphere.
Landfills will continue to produce methane long after trash is deposited, upwards of 25 years.
The design of landfills has come a long way. Thirty years ago, waste management was characterized by dumps, glorified large holes where trash was unceremoniously buried. Now linings and caps eliminate leaching and odor, and recycling and hazardous waste capture are part of the process.
But there is still more to be done. Organic waste management can still be improved upon — a dedicated anaerobic digestor could capture an even larger portion of methane, and greatly extend landfill lifespans by reducing the amount of material that needs to be landfilled. Currently the Madison city council is considering building a dedicated digestor, but the project is still in its infancy. And finding a way to sustainably dispose of plastics has possible solutions as well.
“As we’re looking for our new landfill site, we not just looking for a landfill, we want a sustainable campus. We want something that is diverting additional waste streams to other ends. So one example of that is plastic pyrolysis; its similar to incineration, except its happening in an environment with the absence of oxygen. So really what’s happening is you’re breaking plastic down to its chemical components. And then realigning those chemicals into new products,” said Welch.
But until then, the landfill will continue to grow. The make-up of the trash here is telling. Almost a fifth of what gets deposited here is recyclable material, mostly paper and some plastics. Another fifth is wasted food that was once edible.
“That’s a huge problem. How do we change that paradigm? They say at least a third of food is thrown away,” said Welch. “That’s a lot of wasted resources, the water, the fuel for the tractors to transport it to different facilities, to get it to your home, to refrigerate it, for it to be thrown away. Its a huge environmental impact. And once its thrown away it produces gas emissions at a landfill, right?”
Next for this landfill will come the long period of waiting. The trash will continue to settle, and the hill will slowly sink. Already the older parts of the landfill have lost 15 feet of height. Grass will be introduced to the top, but nothing with deeper roots that could pierce the lining can be allowed to grow. Older landfills, like at Elver Park or near the Alliant Center, were repurposed into dog parks or soccer fields, but nowadays they pile the trash up too high for human use, so the only outlet for the Dane County landfill is nature preserve.
“So we’re responsible for maintaining this in perpetuity. For us specifically we have an agreement with the town of Cottage Grove and the city of Madison, that anything that’s not building or roads already, will be a conservatory,” said Welch. “So you’ll see a lot more settlement, we have to continue to maintain the cap, protect the area, prevent any type of environmental releases. But eventually you’ll have the gas production drop off. You’ll have even the liquids collection dropping off because there is no more degradation going on, and it becomes basically a stable hill at that point.”